The present invention relates to a read head for reading out an information signal from a magnetic storage medium and more particularly, to an improved magnetoresistive read head and a magnetic storage system using the head.
Conventionally, a magnetic read transducer called a magnetoresistive (MR) sensor or head is known. It is also known that such a sensor can read data from a magnetic medium having a large linear density. The MR sensor, which utilizes a variation in the resistance of a read element made of magnetoresistive material, detects a magnetic signal as a function with respect to the magnitude and direction of magnetic flux detected by the element.
It is also known in the prior art that, in order to optimumly operate the MR element, it is necessary to apply two magnetic bias fields to the element. For the purpose of biasing the MR element to linearly respond to magnetic flux, in general, transverse biasing field is used. This biasing field is parallel to the flat surface of the MR element and vertical to the plane of the magnetic medium. There are various ways of applying the transverse biasing field, including current bias, shunt bias, soft bias, and soft adjacent layer (SAL) bias. These transverse biases are generated at such a level as to sufficiently bias the head in the most linear range of its resistivity-magnetic field (R-H) curve.
Among the other biasing magnetic fields used for the MR element, longitudinal bias magnetic field called so by those skilled in the art is parallel to the surface of the magnetic medium and also parallel to the longitudinal direction of the MR element. The longitudinal bias magnetic field acts to suppress Barkhausen noise caused by the multi-domain of the MR element.
Many MR sensor biasing methods and systems have been conventionally developed. However, as the recording density becomes large, it has become necessary to make narrower its recording track and larger a linear density along the track. Such a small MR element as to satisfy the requirements cannot be realized by the prior art methods.
The problem in the prior art has been conceptionally solved by employing a patterned longitudinal biasing. Its solution method is disclosed in JP-A-60-59518. In this invention, in short, the end regions of an MR layer are put in suitable single domain condition so that the single domain condition is induced within the central active region of the MR layer. This can be realized by generating a longitudinal biasing only within the end regions of the MR layer. In the conceptional embodiment, the longitudinal biasing is realized by the ferromagnetic exchange coupling or magnetostatic coupling between a hard magnetic layer and the MR layer.
Also disclosed in JP-A-60-59518 is a method for realizing the longitudinal biasing based on the ferromagnetic coupling when a ferromagnetic layer having a coercivity larger than the MR layer is provided only at the overlapped part of an electrode and the MR layer. In the invention, the MR layer has a thickness of 200-1000 angstroms and the ferromagnetic layer having a larger coercivity has a thickness of 500-3000 angstroms.
In U.S. Pat. No. 5,005,096 (JP-A-2-220213), another method for realizing the longitudinal biasing based on the magnetostatic coupling between a hard magnetic layer and an MR layer is disclosed. In this method, the inherent coercivity of the hard magnetic layer exchange-coupled to the soft magnetic MR layer substantially disappears (which is disadvantageous in the perpetuity of the biasing). In addition, for the purpose of avoiding the adverse influence of the magnetic flux from the hard magnetic layer on a transverse sensitivity profile, the hard magnetic layer is arranged to be parallel to the MR layer and also be spaced from the MR layer. In actual, a non-magnetic spacer layer is inserted between the hard magnetic thin film and the end domain control regions of the MR layer and the thickness of the hard magnetic thin film is selected so that a magnetic flux ratio has a desirable value between the magnetic flux of the end magnetic control regions of the MR layer and the vertical magnetic flux of the central active region of the MR layer. Also explained in the patent is that, to this end, it is preferable that the spacer layer has a thickness of 50-200 nm and the electrically conductive non-magnetic material is Cr, W, Nb or Ta.
In any one of the prior art methods, the inner end faces of the end magnetic control regions directly contacted with the hard magnetic layer coincides with the inner end faces of the electrode or the inner end faces of the electrode are located inside of the inner end faces of the end magnetic control regions, so that the track width of the magnetoresistive element is determined substantially by a distance between the inner end faces of the electrode.
When it is desired to fabricate such a magnetoresistive element on a mass production basis, the center between the inner end faces of the end magnetic domain control regions may be shifted from the center between the inner end faces of the electrode so that one of the inner end faces of the end magnetic control regions is shifted largely outwardly of the associated inner end face of the electrode. When the inner end face of the end magnetic control region is shifted largely outwardly of the associated inner end face of the electrode, the vertical biasing by the hard magnetic layer may not be able to be sufficiently applied to the vicinity of the ends of the electrode. Thus, it sometimes occurs that it is impossible to suppress the generation of magnetic walls induced by stress concentration or the like in the vicinity of the ends of the electrode and thus to suppress Barkhausen noise.